Known systems for multi-level control, e.g. volume control or screen/light brightness control in consumer electronics products, use circular touch-pads or capacitive linear sliders (frequently mounted above the keyboard in notebooks), or they are using the touch information from a generic notebook touchpad when the finger is moving in a dedicated slider area, for example on the right border of the touchpad.
These sensors provide absolute position information about the finger tip, and hence the finger tip's angle on the circular touchpad or the position on the slider—information that can be mapped directly or differentially to a control level in a straight forward way.
In particular for a circular touch-pad it is important that the fingertip position and the touchpad's geometric center build an angle with a reference position, e.g. on the pad's rim, and this angle can be evaluated.
When it comes to the recognition of circle gestures without fix reference position, determining an angle in the circle movement is no longer straight forward. This is the case, for example, for a generic non-circular touchpad, with 2D/3D free-air gestures using near-field capacitive sensor systems, or with mid/far field sensor systems like video or infrared camera systems.
It has to be considered that a circle movement can be either clockwise or counter-clockwise, and it will not be limited to have a fix start or stop position. At each time during the circle movement, for real-time application one can only evaluate data acquired up to the presence, i.e. only partial gesture patterns. Without knowing the drawn circle's center, in the beginning of the movement the detection unit cannot tell the direction of the circle: For example, a left-to-right movement appears in the top of a clockwise circle but also in the bottom of a counter-clockwise circle.